Phase shift modulation system



- y 1950 s. s. KONIGSBERG 2,508,270

PHASE SHIFT MODULATION SYSTEM Filed Jan. 22. 1946 EigLl /9 Q 49 57 V J.

9 I N VENTOR. J/D/VEY J: KOA/IGJZBERG Patented May 16, 1950 om STATES? ear ENT Fl cs:-

2;50zi',2'z0 PhasesmFT-MoDULA'rIoN swsTEM Sidney S.- Konigsberg, San Francisco Galif as signor to John M. Kaar doingi husinessasK-aar- Engineering. compan Pal'o Jilto, Califl AppIiatioriJaRuary -ZZ, 194s, Serial-Notfiflgflitf:

(Cl. 332',Z3

invention: relates-to; modulation of highfrequency. radios energy and more: particularly. to a; system;v for phase shift modulation arising; outrofi. the phase? modulation or: the output: of a source ofzhigh frequency energy.

Among the objectsofnmminvention are: (1);; To provide: as noveleand improved; system oflmodulationa V .0294 Tognorideagvnovelpandrimproved system Ofifphaseishif-t; modulationt (3); Toiprovides-aa novels and; improvedi system: ota phase. shirt modulationeapplicable to electron discharge devices haying buta single control grid; 7 r (4) Ila-provide 1:9,; novel?andaimprpvedasystem of phase: shift modulation: characterized; loyv a minimumzof;distortiona Tea-provide a: novel and improved system* otkphaseishiftemodulationuvhich:is simple in; the matter-0t i cu tdesien and efficient mace a o a: 6) 'TI 0:-.p 0vid nov lr nd; mpr edy em of phase shift modulation capable of utilizing electron;dischargedevioes: ofri the; instantheating ime; (7 To-provide;avnovelar d improved= methodaotlmedulating high ireqnencxenergy; v 'Iqoeprovide a novel-and; improved method; at;iqhasa-sh fi m lat na i r r n ner y- Additional. objects, of; my invention; will he broughtout inrthe followingsv description of: a

wnl'llnction withqthe accompanying drawings w er 4 Figure -1 is a oircuit diagram illustratinga;- preferred embodimenteof my novel and-improved? modulation systemg; I I

Figure 2 is a vector diagliamaillustratingi therelationship ofitvoltagesi -iata ghasesselittin 'petwork lformihg an important-component oi the: circuit;of,1 igl .4i-l1';n Y J i A A H Figurest3a,-\. 3b.: andwiicflare related yectortdiagrams illustratingthe manner; o f,-.1-ealizing phase shift modulatiorr-l-in response: to: the appli c of, modulating-4. vo qages ins; myf aforementi ir t e The, system" of.- my, inyeritionr-iscomposed of Variouseomponents-including all scillatort I 4 at phase:splitting networkL3vcoopera therewith to prodi lc'e a pair? of "fvoltagesz oil 'subst" tiallyv the same magnitudetbutsufistantiallfi schemes out oi'fpllaseiwithlgone another andg ope1 atih'g;-- about eeeommon point in vthe circuit a phase modulater; 51th! which suchxvoltagese-are appliem and aljmicrophone and: amplifier oombination. 1 for m dulatihg the;outputr oi the aforementioned swimwe oned' The oscillator may: basically be oi anyv conventiona-l type designed for putting out energy at; arstabilizedfrequency but; is slightly modifiedto accommodate it to the system-1ofmy iriventiom;

That-v oscillator illustrated; by me is: one of many crystal-controlled oscillators adaptable for use -in- -my--circuit,- and comprises an electron dis charge device or tube 9-having1 cathode l"-l gr-icl i3; anol plate I5 electrodes; with a condenser shunted-- resistor H in the input" circuit between the cathodeand grid and a tank circuit 19 connected in? the output circuit of the tube it bein noted, l'ioweverinthis connections that the connection ta the cathode is from the; mid

4 point-2+ of the tank coil it by way of a radio" frequency: by-passcondenser 25; ar1dnot fromthe lower end: of' the tanks circuit as isconven tiorial practices 1n asemuch as the cathode; grounded, this -places the midpoint- 2| at" highfrequencyv ground potential V m Blate yoltage isapplied; by wayof theupper hall ofithe-tank'coi-lirom a source ot plate potential, in this case a dynamotbnincluding: a-gener-= ator Zldriven-by a=moton 29 such dy-nan gtor; serving" as a-source-ot-platepotential for all the: electro discharge devices-in.-the system.

A crystal 31* ot the desired-frequency is :COlEle'j nectedbetweem the? control electrode and the; plate and t suchgcrystal, .v together with the tankq circuit which tunedq to the frequency of the crystal will cause the: oscillator to function as such andsat a stabil-ized frequency. 7 a

The particular tuloe illustratedincludesgalso a-;conventional.-:typa soreenegrid", electrode 33-5 to:-

which the proper operating potential; is applied from the plate supply source througlr a voltage droppinesresiston 35 -properly by -passedi at radio frequency; and a beamiorming -plate;37;=between-- the plate and the screen grid and corinecteddnthe conve tio al manner torthe cathode.

Across rthe tankwircuit issconne'o'tedthe phase splittings circuit: 3 comprising a-- series c onnected resistor 39 and cohdenser H of similar ohmicvalueat the} frequenoyof the" oscillator; for-1 example, Xc eq la sR-dn terms -ofiohms ats-the frequency at whichthe oscillator-'functions." A blocking condenser 43 between themesistoeand theupper-end or the/tankcircuit serve's to isolate the phases-splittings circuit; "from the direct cur rent pIate voltage applied to the oscillator tubes This blocking condenser, however, bei-fi'gfiof such low impedance;- to'" current at -the' oscillator frequency t may for all practicalepurposes be C011? s ider-ed asr non-existent insofanas thehiglrfre v quency efiectsrin the system:are concerned:

modulator.

The phase modulator 5 comprises a pair of electron discharge devices or tubes 45 and 41 of similar type and preferably of the type employed in the oscillator. These discharge devices have their cathodes connected together and grounded, while the grid of the tube 45 is connected through a coupling condenser 49 to the upper end of the oscillator tank circuit, and the gridof the other tube 41 is connected to a point 5| intermediate the condenser 41 and resistor 39 of the phasesplitting circuit.

In the case of each of the phase modulator tubes, bias on the grid is derived from a selfbiasing combination. Relative to the tube 45,

such self-biasing combination involves a resistor 53 connected between the grid and ground and by-passed by the coupling condenser 49.

In the case of the other tube 47, the bias is derived across a similarly connected resistor 55 by-passed by the phase-splitting circuit condenser 4|. The values of the resistors 53 and 55 are adjusted to bias the phase modulator tubes for Class C operation in response to grid rectification of the oscillator voltage.

Class C operation may be defined as Amplification by means of electron tubes wherein the grid bias is made greater than the cut-off value corresponding to the plate supply voltage, so that when a signal is applied, plate current flows in pulses that last for less than half a cycle.

Relative to the coupling condenser 49, this condenser also functions to by-pass the A. C. component of the current which would otherwise pass through the biasing resistor 53.

connected in parallel at high frequency, to a common output or tank circuit 51. Plate voltages are applied from the common source of plate voltage, the high voltage end of which connects to the midpoint 59 of a center tapped secondary winding 61 of an audio transformer 53. One end-of this secondary winding connects to the lower end of the coil 65 of the tank circuit 51, which tank oil completes the plate voltage circuit to the plate of the tube 45 of the phase modulator. The other end of the secondary winding is connected to the plate of the other tube 41 of the phase modulator through a radio frequency choke coil 61. A- blocking condenser 69 between this Plate and the upper end of the tank circuit serves to isolate the two direct current plate voltage circuits, without disturbing the parallel connection of the plates to the tank cir- Modulating potentials are introduced into the direct current plate voltage circuits of the phase modulator equally and oppositely, from a microphone circuit H by way of an audio amplifier 13 in whose output circuit is connected the primary winding 15 of the audio transformer.

The amplifier may be of-any conventional design. That illustrated' employs an electron discharge device ll similar to those previously described as embodied in the oscillator and phase The grid is connected to a voltage divider 19 which is in series with a high audiofrequency deemphasizing condenser 8! across the secondary 83 of an input audio transformer 85, which in turn couples the microphone circuit to the amplifier.

The plate of the amplifier tube connects to the source of plate voltage through the primary of the output transformer. Fixed bias is derived from a resistor 81 connected between ground and the negative end of the plate voltage generator.

In analyzing the operation of my improved system, it will be necessary to refer back to the phase splitting circuit 3 and note the part it plays in the proper functioning of my invention.

It is known that an alternating current through a condenser will lead the voltage which produces it, by approximately degrees, while the same current through a resistor will be in phase with the voltage across the resistor. Consequently, in a series arrangement of a resistor and condenser as shown, where the current is the reference factor, the voltage across the resistor and that across the condenser will be approximately 90 degrees out of phase. Assuming each element presents the same ohmic resistance to the flow of current therethrough, the voltage vectors will be of the same length.

The phase-splitting circuit which includes the condenser 4| and resistor 39, being connected across the tank circuit IQ of the oscillator, the vector sum of the voltage drops across said condenser and resistor, neglecting the insignificant drop across the blocking condenser 43, will equal that across the tank circuit.

The voltage relationships, therefore, when reresented vectorially, will show up as a right angle isosceles triangle ab-c as illustrated in Figure 2, wherein the hypotenuse a-c represents the tank voltage and the shorter but equal sides a.b and 17-0 represent the voltage drop across the condenser and resistor, respectively.

1 It is of interest to note in this connection, that th center tap 2| on the tank coil 23 being grounded, it constitutes a fixed reference point through which the carrier frequency voltage oscillates at the frequency of the oscillator, and that this same point corresponds to the middle point d on the tank voltage vector a-c of Figure 2.

A vector d-b drawn from this midpoint to the junction of the two shorter vectors will, therefore, represent the voltage between the grounded enter tap 2i on the tank coil and the point of connection 5i between the condenser and resistor of the phase-splitting circuit. The magnitude and phase of this voltage will be as shown in the vector diagram of Figure 2 and will, therefore, be equal to one-half the tank voltage in magnitude and will be displaced therefrom by an angle of 90 degrees. Either half of the tank voltage and the vector joining the center point to the apex of the triangle will operate about the same point 01 representing the grounded center point on the tank coil 23.

Thus through the combination of the oscillator and phase-splitting circuit, connected as described, I am able to obtain a pair of voltages at highfrequency operating about a common point at ground potential and substantially 90 degrees phase relationship to one another.

One of these two voltages will, therefore, be impressed between the grid and cathode of one of the phase modulator tubes, for example, the tube 45, while the other voltage will be impressed between the grid and cathode of the other tube 41' of the phase modulator tubes. In the absence of any impressed modulating voltages upon the plate circuits of the modulator tubes, the output voltages developed in the common tank circuit 51 0f the phase modulator will be of substantially equal magnitude but 90-degrees out of phase with each other, and will combine vectorially in the tank circuit to produce a resulting voltage displaced: 45: degrees from. I eitheri ofir itscompo-Q,v neg;

Thisrelationship. isshown in Figurev 3aiwhere= lnrthehtwo; componentvoltages; e1) and" f;g are on: the. same magnitude; but. 90. degrees out of: phasewithrespect to each other, while the rea sultant. voltage vector firs-h will lie on the 45 degreeiline and will: be of; a. magnitude equal tothe squareroot, of: the sum of: the squaresof the, component voltages or lAltimes the magnitude of either of the component; vectors.

Assume now that. an alternatingmurrentmodulatings voltage were applied across, the. center: tapped-secondary winding, of; the, audio. amplifier; transformer. At-agiven instant, under such condttions; the plate voltage applied to one of; the,

phase;.modul;ator tubeswill increase by half't-he,

valuaof-such applied voltage, while the plate voltage on the, other phase modulator tube will decrease by asimilar amount, The output of the phaseimodulator tubes will vary accordingly, and since these tubes are operating class C, the changes will be linear and will be represented by linear changes in the magnitudes of thevoltage vectors; and we will assume that such changes occurred: in. the direction indicated in the; vector diagram ofFigure 3b.

It willbenoted by reference'to this vector diagraI-mand-by comparison with that of Figure 3a, thatethe. resultant voltage vector has shifted from th8 .4\5 degreeposition to aposition approaching thelonger: vector e-f of the two component voltagevectors;

On the succeeding half-cycle of: modulating-p91 tential, conditions will be reversed as represented; byitheivector diagram of Figure 3c, wherebyv the resultant voltage vector, f-.-h will swing. back, acrossthe. 45 degree position representing thena modulation. position, toward the other compo-e nent voltage vector f-g.

From the above, itwill become apparent, that in response to modulating potentialsappliedto; the plate circuits of the phasemodulation tubes, as: described, the phase of the resultant voltage vector will shiftfromoneside to the, other of; the 451degree11ine and that the extent of suchswing: willgvaryiwith the magnitudeof the modulating; potentials;

It;is known and can be demonstrated math'ee matically, that: a transient phase shift in a car--. rier frequency is. the equivalent of a transient. change ini requeneyw of the carrier, and accord-V ingly if; the resultant voltage developed across. the.

tanle vcircuit of the phase modulator is. impressed upon atransm-ittingantenna, either directly orthrough an intervening amplifier, it will here-.1, ceivableiasra frequencymodulated carrier.v

It is ofainteresttm note in connection with the, vector diagrams of Figures 3a, 3band 30, that within the practical operating limits of thetuhes:

in the; circuit, the maximum extent ,of swing of theresultant. voltage, vector will in any event be, rather small and, within such limits, the magniev tude'zof; the resultant voltage vector can change;

but;only;- an; insignificant amount. For all practical purposes, therefore, such changes-in the; magnitude: of the resultant voltage across the;

tank. circuit. of the phase modulator may ordi-U narily.- be disregarded. Such changes, howeven may; desired, be, effectively avoided by the insertion of'a resistor 89 in each, plate, voltage sup-V ply circuit to the phase modulator; Each resistorshould: preferably beof a value such that a modu-.-. lating; pulsesufiicient. to erase one compone vector ands-double the len th or other;

, itednumber of grid too ew h, fact: to; e ethe circuit; of, an instant. heating. ypeube, at;v

presentavailable clo he. mar setwith ly alimsuch ube to. be utilized ri kn wn phase s ift modlflatiha i euita n. rior a y te s f; odula ion ub s of; t ermultil ari nwhere the e J en s. are. oi the owhe t heiy e, i is' ce sart tomaintainpoweron the filament at all-times.

o-that heahnar tuamevb av i abl iq ns ant;- use.

Such ieth lsiu tieo,which p v i s n; oh eoa en wi her-tab er ahsmit ers, such s arece a e n; rov n Police ar n t: ires.,-no. r t of he; magi a ion topp ec tehe heavy drain, on thetcar battery which such installation entails. i

In making it possible to" utilize instantheater,v

type tubes, power need be applied to thefilament through, the armature. 93, and, contact 950i a;

normally open relayr-9fl Likewise, the, negative brush oi, the, motor 29, is connected to the negative terminal of the. battery, while. the positivev brush is connectable. to the positive terminal, of, the battery. through. the same armature, and contact, whereby when,

such armature is: pulled into engagement with. the contact, both the, filaments and the motor are-c n ed. s h attery a d simul neously energized there Home.

To efie ct- .sl1ch,connection,;the, relay, conc l v a she atte z-y thro eha al oper-able starting switchuali, which in an actual installation will be under,- control oi an operator,

whereby a mere; closure of; theswitch will im? mediately energize: the apparatus and. place it, in,

condition for; operation.

In a conventional systemoithe general type to which the invention relates, where the fre.- quency of transmission is high, the, oscillator will be designed for operationv at av relatively low frequency. andthe frequency multiplied through,

the utilization. of,- a. plurality of, stages officer. quency multiplication In the system, of the,.presentinvention, while the tank circuit 51 might be tuned, to. the fre quency of the oscillator, it is preferred to. tune.

it to; aharmonic thereof, for'by sodoing it will, be possible to causetthe; modulator to take onthe added functionof a frequency'multiplier,

whereby one stage of frequency multiplication),

may be; eliminated.

While I have described; my invention in con a siderabledetail in, its-preferred, embodiment, the;

same is subject to alteration andr modification, without departing; fromthe; underlying: princie.

pies thereof, and; I accordingly do, not,- esil r t ee-limited: n a Refl tion o hesheei a.

details illustrated and described, except as may be necessitated by the appended claims.

I claim.

l. A modulation system comprising a high-frequen-cy source, a tank circuit associated with the output circuit'of said high-frequency source, said tank circuit having a connection from a midpoint thereon, a phase splitting circuit connected in parallel to said tank circuit and including a resistor and impedance in series, said resistor and impedance being of like ohmic resistance at the frequency of said tank circuit, a modulator including a pair of control grid and plate electrodes and cathode means forsaid control grid and plate electrodes, means coupling one of said control grid electrodes to one end of said tank circuit, means coupling the other of said control grid electrodes to a point on said phase splitting circuit intermediate said resistor and impedance, means vectorially combining the high frequency voltages applied to said control grid electrodes as amplified in said modulator, to obtain a resultant voltage, and means for shifting the phase position of said resultant voltage with respect to its components, in accordance with modulating voltages.

2. A modulation system comprising a highfrequency source, a' tank circuit associated with the output circuit of said high-frequency source, said tank circuit including a tank coil in parallel with a condenser and having a connection from a midpoint thereon at high frequencies, a phase splitting circuit connected in parallel to said tank circuit and including a resistor and impedance in series, said resistor and impedance being of like ohmic resistance at the frequency of said tank circuit, a modulator including a pair of similar electron discharge devices, each having a cathode, a control grid electrode and a plate electrode, said cathodes being connected to said tank circuit midpoint, means coupling the control grid electrode of one of said electron discharge devices to one end of said tank circuit, means coupling the control grid electrode of the other of said electron discharge devices to a point on said phase splitting circuit intermediate said resistor and impedance, means coupling the output circuits of said electron discharge devices to vectorially add high frequency voltages appearing in said output circuits, and means for introducing into said output circuits modulation voltages with the modulation voltages in the one such circuit of substantially the same amplitude as but of opposite polarity from the corresponding modulation voltages in the other of said output circuits.

3; A modulation system comprising a highfrequency source, a tank circuit in the output circuit of said high-frequency source said tank circuit including a tank coil in parallel with a condenser and having a connection from a mid- .point thereon at high frequencies, a phase splitting circuit connected in parallel to said tank circuit and including a resistor and condenser in series, said resistor and condenser being of like ohmic resistance at the frequency of said tank circuit, a modulator including a pair of similar electron discharge devices, each having a cathode, a control grid electrode and a plate electrode, said cathodes bein connected to said tank circuit midpoint, means coupling the control grid electrode of one of said electron discharge devices to the upper end of said tank circuit, means coupling the control grid electrode of the other of said electron discharge devices to a point on said phase splitting circuitintermediate said resistor and condenser, means coupling the output circuits of'said electron discharge devices'to vectorially add high frequency voltages appearing in said output circuits, and means for introducing into said output circuits modulation voltages with the modulation voltages in the one such circuit of substantially the same amplitude as but of opposite polarity from the corresponding modulation voltages in the other of said output circuits.

-4. A modulation system comprising a highfrequency oscillator, a tank circuit in the output circuit of said oscillator, said tank circuit including a tank coil in parallel with a condenser and having a connection from a midpoint thereon "to ground at high frequencies, a phase splitting circuit connected in parallel to said tank circuit and including a resistor and condenser in series,

said resistor and condenser being of like ohmic resistance at the frequency of said tank circuit, a modulator including a pair of similar electron discharge devices, each having a cathode, a control grid electrode and a plate electrode, said cathodes being grounded, means coupling the control grid electrode of one of said electron discharge devices to the upper end of said tank circuit, means coupling the control grid electrode of the other or" said electron discharge devices to a point on said phase splitting circuitintermediate said resistor and condenser, means coupling the output circuits of said electron discharge devices to vectorially add high frequency voltages appearing in said output circuits, and means for introducing into said output circuits modulation voltages with the modulation voltages in the one such circuit of substantially the same amplitude as but of opposite polarity from the corresponding modulation voltages in the other of said output circuits.

5. In a phase shift modulation system, a pair of modulator tubes, each having a cathode, a control grid electrode and a plate electrode, an input circuit coupling the cathode and control electrode of one of said tubes, an input circuit coupling the cathode and control electrode of the other of said tubes, a high frequency output circuit for each of said tubes between the plate electrode thereof and its cathode and including a tank circuit in common, with both said plate electrodes connected at high frequency to the same end of said tank circuit, a circuit for applying direct current voltage to each of said plate electrodes, and means for introducing into each of said direct current voltage-applying circuits modulating voltages of substantially like magnitude, but with the modulating voltages in one of said circuits of opposite polarity with respect to those modulating voltages in the other of said circuits.

6. In a phase shift modulation system, a pair of modulator tubes, each having a cathode, a control grid electrode and a plate electrode, an input circuit coupling the cathode and control electrode of one of said tubes, an input circuit coupling the cathode and control electrode of the other of said tubes, a high frequency output circuit for each of said tubes between the plate electrode thereof and its cathode, a tank circuit, means associating said tank circuit with both said output circuits, said means including high frequency connections from said plate electrodes to the same end of said tank circuit, a circuit for applying direct current voltage to each of said plate electrodes, means for introducing into each 9 of said direct current voltage-applying circuits modulating voltages of substantially like magnitude, but with the modulating voltages in one of said circuits of opposite polarity with respect to those modulating voltages in the other of said circuits, and a voltage dropping resistor in each of said direct current voltage-applying circuits.

'7. In a phase shift modulation system, a pair 01' modulator tubes, each having a cathode, a control grid electrode and a plate electrode, an input circuit coupling the cathode and control electrode of one of said tubes, an input circuit coupling the cathode and control electrode of the other of said tubes, a high frequency output circuit for each of said tubes between the plate thereof and its cathode and including a tank circuit in common, with both said plate electrodes connected at high frequency to the same end of said tank circuit, a circuit for applying direct current voltage to each of said plate electrodes, means for introducing into each of said direct current voltage-applying circuits modulating voltages of substantially like magnitude, but with the modulating voltages in one of said circuits of opposite polarity with respect to those modulating voltages in the other of said circuits, and a voltage dropping resistor in each of said direct current voltage-applying circuits.

8. A modulation system comprising a class-C radio frequency amplifier involving a pair of electron discharge devices each including cathode, grid, and anode electrodes, means for applying to each of said grid electrodes, radio frequency voltage substantially out of phase with the voltage applied to the other grid electrode; a, tank circuit having a resonant frequency in the radio frequency range, means connecting said anodes in parallel to one end of said tank circuit, and a connection to ground from the other end of said tank circuit; and means for plate modulating said class-C amplifier.

10 9. A modulation system comprising a class-C radio frequency amplifier involving a pair of electron discharge devices each including cathode, grid, and anode electrodes, a tank circuit having a resonant frequency in the radio frequency range, means connecting said anodes in parallel to one end of said tank circuit, and a connection to ground from the other end of said tank circuit; and means for plate modulating said class-C amplifier, said means including an audio frequency amplifier having a center-tapped output transformer winding, one end of said winding being connected to one end of said tank circuit, the other end of said winding being connected to said anodes, and a source of direct current voltage connected to the center tap of said winding.

10. A modulation system comprising a class-C radio frequency amplifier involving a pair of electron discharge devices each including cathode, grid, and anode electrodes, means for applying to each of said grid electrodes, radio frequency voltage substantially out of phase with the voltage applied to the other grid electrode; a tank circuit having a resonant frequency at a harmonic of the grid applied voltage, means connecting said anodes in parallel to a point on said tank circuit, and a connection to ground from another point on said tank circuit; and means for plate modulating said class-C amplifier.

SIDNEY S. KONIGSBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,049,143 Usselman July 28, 1936 2,165,229 Crosby July 11, 1939 2,220,201 Bliss Nov. 5, 1940 

